Documentation/intro-quick.txt - gerrit - Git at Google

 Gerrit Code Review - A Quick Introduction
 =========================================

 Gerrit is a web-based code review tool built on top of the git version
 control system, but if you've got as far as reading this guide then
 you probably already know that. The purpose of this introduction is to
 allow you to answer the question, is Gerrit the right tool for me?
 Will it fit in my work flow and in my organization?

 What is Gerrit?
 ---------------

 I assume that if you're reading this then you're already convinced of
 the benefits of code review in general but want some technical support
 to make it easy. Code reviews mean different things to different people.
 To some it's a formal meeting with a projector and an entire team
 going through the code line by line. To others it's getting someone to
 glance over the code before it is committed.

 Gerrit is intended to provide a light weight framework for reviewing
 every commit before it is accepted into the code base. Changes are
 uploaded to Gerrit but don't actually become a part of the project
 until they've been reviewed and accepted. In many ways this is simply
 tooling to support the standard open source process of submitting
 patches which are then reviewed by the project members before being
 applied to the code base. However Gerrit goes a step further making it
 simple for all committers on a project to ensure that changes are
 checked over before they're actually applied. Because of this Gerrit
 is equally useful where all users are trusted committers such as may
 be the case with closed-source commercial development. Either way it's
 still desirable to have code reviewed to improve the quality and
 maintainability of the code. After all, if only one person has seen
 the code it may be a little difficult to maintain when that person
 leaves.

 Gerrit is firstly a staging area where changes can be checked over
 before becoming a part of the code base. It is also an enabler for
 this review process, capturing notes and comments about the changes to
 enable discussion of the change. This is particularly useful with
 distributed teams where this conversation can't happen face to face.
 Even with a co-located team having a review tool as an option is
 beneficial because reviews can be done at a time that is convenient
 for the reviewer. This allows the developer to create the review and
 explain the change while it is fresh in their mind. Without such a
 tool they either need to interrupt someone to review the code or
 switch context to explain the change when they've already moved on to
 the next task.

 This also creates a lasting record of the conversation which can be
 useful for answering the inevitable "I know we changed this for a
 reason" questions.

 Where does Gerrit fit in?
 -------------------------

 Any team with more than one member has a central source repository of
 some kind (or they should). Git can theoretically work without such a
 central location but in practice there is usually a central
 repository. This serves as the authoritative copy of what is actually in
 the project. This is what everyone fetches from and pushes to and is
 generally where build servers and other such tools get the source
 from.

 .Central Source Repository
 image::images/intro-quick-central-repo.png[Authoritative Source Repository]

 Gerrit is deployed in place of this central repository and adds an
 additional concept, a store of pending changes. Everyone still fetches
 from the authoritative repository but instead of pushing back to it,
 they push to this pending changes location. A change can only be submitted
 into the authoritative repository and become an accepted part of the project
 once the change has been reviewed and approved.

 .Gerrit in place of Central Repository
 image::images/intro-quick-central-gerrit.png[Gerrit in place of Central Repository]

 Like any repository hosting solution, Gerrit has a powerful
 link:access-control.html[access control model.]
 Users can even be granted access to push directly into the central
 repository, bypassing code review entirely. Gerrit can even be used
 without code review, used simply to host the repositories and
 controlling access. But generally it's just simpler and safer to go
 through the review process even for users who are allowed to directly
 push.

 The Life and Times of a Change
 ------------------------------

 The easiest way to get a feel for how Gerrit works is to follow a
 change through its entire life cycle. For the purpose of this example
 we'll assume that the Gerrit Server is running on a server called
 +gerrithost+ with the HTTP interface on port +8080+ and the SSH
 interface on port +29418+. The project we'll be working on is called
 +RecipeBook+ and we'll be developing a change for the +master+ branch.

 Cloning the Repository
 ~~~~~~~~~~~~~~~~~~~~~~

 Obviously the first thing we need to do is get the source that we're
 going to be modifying. As with any git project you do this by cloning
 the central repository that Gerrit is hosting. e.g.

 ----
 $ git clone ssh://gerrithost:29418/RecipeBook.git RecipeBook
 Cloning into RecipeBook...
 ----

 Then we need to make our actual change and commit it locally. Gerrit
 doesn't really change anything here, this is just the standard editing
 and git. While not strictly required, it's best to include a Change-Id
 in your commit message so that Gerrit can link together different
 versions of the same change being reviewed. Gerrit contains a standard
 link:user-changeid.html[Change-Id commit-msg hook]
 that will generate a unique Change-Id when you commit. If you don't do
 this then Gerrit will generate a Change-Id when you push your change
 for review. But because you don't have the Change-Id in your commit
 message you'll need to manually copy it in if you need to upload
 another version of your change. Because of this it's best to just
 install the hook and forget about it.

 Creating the Review
 ~~~~~~~~~~~~~~~~~~~

 Once you've made your change and committed it locally it's time to
 push it to Gerrit so that it can be reviewed. This is done with a git
 push to the Gerrit server. Since we cloned our local repository
 directly from Gerrit it is the origin so we don't have to redefine the
 remote.

 ----
 $ <work>
 $ git commit
 [master 9651f22] Change to a proper, yeast based pizza dough.
  1 files changed, 3 insertions(+), 2 deletions(-)
 $ git push origin HEAD:refs/for/master
 Counting objects: 5, done.
 Delta compression using up to 8 threads.
 Compressing objects: 100% (2/2), done.
 Writing objects: 100% (3/3), 542 bytes, done.
 Total 3 (delta 0), reused 0 (delta 0)
 remote:
 remote: New Changes:
 remote:   http://gerrithost:8080/68
 remote:
 To ssh://gerrithost:29418/RecipeBook.git
  * [new branch]      HEAD -> refs/for/master
 ----

 The only different thing about this is the +refs/for/master+ branch.
 This is a magic branch that creates reviews that target the master
 branch. For every branch Gerrit tracks there is a magic
 +refs/for/<branch_name>+ that you push to to create reviews.

 In the output of this command you'll notice that there is a link to
 the HTTP interface of the Gerrit server we just pushed to. This is the
 web interface where we will review this commit. Let's follow that link
 and see what we get.

 .Gerrit Code Review Screen
 image::images/intro-quick-new-review.jpg[Gerrit Review Screen]

 This is the Gerrit code review screen where someone will come to
 review the change. There isn't too much to see here yet, you can look
 at the diff of your change, add some comments explaining what you did
 and why, you may even add a list of people that should review the change.

 Reviewers can find changes that they want to review in any number of
 ways. Gerrit has a capable
 link:user-search.html[search]
 that allows project leaders (or anyone else) to find changes that need
 to be reviewed. Users can also setup watches on Gerrit projects with a
 search expression, this causes Gerrit to notify them of matching
 changes. So adding a reviewer when creating a review is just a
 recommendation.

 At this point the change is available for review and we need to switch
 roles to continue following the change. Now let's pretend we're the
 reviewer.

 Reviewing the Change
 ~~~~~~~~~~~~~~~~~~~~

 The reviewer's life starts at the code review screen shown above. He
 can get here in a number of ways, but for some reason they've decided
 to review this change. Of particular note on this screen are the two
 "Need" lines:

 ----
 * Need Verified
 * Need Code-Review
 ----

 Gerrit's default work-flow requires two checks before a change is
 accepted. Code-Review is someone looking at the code, ensuring it
 meets the project guidelines, intent etc. Verifying is checking that
 the code actually compiles, unit tests pass etc. Verification is
 usually done by an automated build server rather than a person. There
 is even a
 link:https://wiki.jenkins-ci.org/display/JENKINS/Gerrit+Trigger[Gerrit Trigger Jenkins Plugin]
 that will automatically build each uploaded change and update the
 verified score accordingly.

 It is important to note that Code-Review and Verification are
 different permissions in Gerrit, allowing these tasks to be separated.
 For example, an automated process would have rights to verify but not
 to code-review.

 Since we are the code reviewer, we're going to review the code. To do
 this we can view it within the Gerrit web interface as either a
 unified or side-by-side diff by selecting the appropriate option. In
 the example below we've selected the side-by-side view. In either of
 these views you can add inline comments by double clicking on the line
 (or single click the line number) that you want to comment on. Also you
 can add file comment by double clicking anywhere (not just on the
 "Patch Set" words) in the table header or single clicking on the icon
 in the line-number column header. Once published these comments are
 viewable to all, allowing discussion of the change to take place.

 .Side By Side Patch View
 image::images/intro-quick-review-line-comment.jpg[Adding a Comment]

 Code reviewers end up spending a lot of time navigating these screens,
 looking at and commenting on these changes. To make this as efficient
 as possible Gerrit has keyboard shortcuts for most operations (and
 even some operations that are only accessible via the hot-keys). At
 any time you can hit the +?+ key to see the keyboard shortcuts.

 .Gerrit Hot Key Help
 image::images/intro-quick-hot-key-help.jpg[Hot Key Help]

 Once we've looked over the changes we need to complete reviewing the
 submission. To do this we click the _Review_ button on the change
 screen where we started. This allows us to enter a Code Review label
 and message.

 .Reviewing the Change
 image::images/intro-quick-reviewing-the-change.jpg[Reviewing the Change]

 The label that the reviewer selects determines what can happen next.
 The +1 and -1 level are just an opinion where as the +2 and -2 levels
 are allowing or blocking the change. In order for a change to be
 accepted it must have at least one +2 and no -2 votes.
 Although these are numeric values, they in no way accumulate;
 two +1s do not equate to a +2.

 Regardless of what label is selected, once the _Publish Comments_
 button has been clicked, the cover message and any comments on the
 files become visible to all users.

 In this case the change was not accepted so the creator needs to
 rework it. So let's switch roles back to the creator where we
 started.

 Reworking the Change
 ~~~~~~~~~~~~~~~~~~~~

 As long as we set up the
 link:user-changeid.html[Change-Id commit-msg hook]
 before we uploaded the change, re-working it is easy. All we need
 to do to upload a re-worked change is to push another commit that has
 the same Change-Id in the message. Since the hook added a Change-ID in
 our initial commit we can simply checkout and then amend that commit.
 Then push it to Gerrit in the same way as we did to create the review. E.g.

 ----
 $ <checkout first commit>
 $ <rework>
 $ git commit --amend
 $ git push origin HEAD:refs/for/master
 Counting objects: 5, done.
 Delta compression using up to 8 threads.
 Compressing objects: 100% (2/2), done.
 Writing objects: 100% (3/3), 546 bytes, done.
 Total 3 (delta 0), reused 0 (delta 0)
 To ssh://gerrithost:29418/RecipeBook.git
  * [new branch]      HEAD -> refs/for/master
 ----

 Note that the output is slightly different this time around. We don't
 get told about a new review because we're adding to an existing
 review. Having uploaded the reworked commit we can go back into the
 Gerrit web interface and look at our change.

 .Reviewing the Rework
 image::images/intro-quick-review-2-patches.jpg[Reviewing the Rework]

 If you look closely you'll notice that there are now two patch sets
 associated with this change, the initial submission and the rework.
 Rather than repeating ourselves lets assume that this time around the
 patch is given a +2 score by the code reviewer.

 Trying out the Change
 ~~~~~~~~~~~~~~~~~~~~~

 With Gerrit's default work-flow there are two sign-offs, code review
 and verify. Verifying means checking that the change actually works.
 This would typically be checking that the code compiles, unit tests
 pass and similar checks. Really a project can decide how much or
 little they want to do here. It's also worth noting that this is only
 Gerrit's default work-flow, the verify check can actually be removed
 or others added.

 As mentioned in the code review section, verification is typically an
 automated process using the
 link:https://wiki.jenkins-ci.org/display/JENKINS/Gerrit+Trigger[Gerrit Trigger Jenkins Plugin]
 or similar. But there are times when the code needs to be manually
 verified, or the reviewer needs to check that something actually works
 or how it works. Sometimes it's just nice to work through the code in a
 development environment rather than the web interface. All of these
 involve someone needing to get the change into their development
 environment. Gerrit makes this process easy by exposing each change as
 a git branch. So all the reviewers need to do is fetch and checkout that
 branch from Gerrit and they will have the change.

 We don't even need to think about it that hard, if you look at the
 earlier screen shots of the Gerrit Code Review Screen you'll notice a
 _download_ command. All we need to do to get the change is copy
 paste this command and run it in our Gerrit checkout.

 ----
 $ git fetch http://gerrithost:8080/p/RecipeBook refs/changes/68/68/2
 From http://gerrithost:8080/p/RecipeBook
  * branch            refs/changes/68/68/2 -> FETCH_HEAD
 $ git checkout FETCH_HEAD
 Note: checking out 'FETCH_HEAD'.

 You are in 'detached HEAD' state. You can look around, make experimental
 changes and commit them, and you can discard any commits you make in this
 state without impacting any branches by performing another checkout.

 If you want to create a new branch to retain commits you create, you may
 do so (now or later) by using -b with the checkout command again. Example:

   git checkout -b new_branch_name

 HEAD is now at d5dacdb... Change to a proper, yeast based pizza dough.
 ----

 Easy as that, we now have the change in our working copy to play with.
 You might be interested in what the numbers of the refspec mean.

 * The first *68* is the id of the change +mod 100+.  The only reason
 for this initial number is to reduce the number of files in any given
 directory within the git repository.
 * The second *68* is the full id of the change. You'll notice this in
 the URL of the Gerrit review screen.
 * The *2* is the patch-set within the change. In this example we
 uploaded some fixes so we want the second patch set rather than the
 initial one which the reviewer rejected.

 Manually Verifying the Change
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 For simplicity we're just going to manually verify the change.
 The Verifier may be the same person as the code reviewer or a
 different person entirely. It really depends on the size of the
 project and what works. If you have Verify permission then when you
 click the _Review_ button in the Gerrit web interface you'll be
 presented with a verify score.

 .Verifying the Change
 image::images/intro-quick-verifying.jpg[Verifying the Change]

 Unlike the code review the verify check doesn't have a +2 or -2 level,
 it's either a pass or fail so all we need for the change to be
 submitted is a +1 score (and no -1's).

 Submitting the Change
 ~~~~~~~~~~~~~~~~~~~~~

 You might have noticed that in the verify screen shot there are two
 buttons for submitting the score _Publish Comments_ and _Publish
 and Submit_. The publish and submit button is always visible, but will
 only work if the change meets the criteria for being submitted (I.e.
 has been both verified and code reviewed). So it's a convenience to be
 able to post review scores as well as submitting the change by clicking
 a single button. If you choose just to publish comments at this point then
 the score will be stored but the change won't yet be accepted into the code
 base. In this case there will be a _Submit Patch Set X_ button on the
 main screen. Just as Code Review and Verify are different operations
 that can be done by different users, Submission is a third operation
 that can be limited down to another group of users.

 Clicking the _Publish and Submit_ or _Submit Patch Set X_ button
 will merge the change into the main part of the repository so that it
 becomes an accepted part of the project. After this anyone fetching
 the git repository will receive this change as a part of the master
 branch.

 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]
	Gerrit Code Review - A Quick Introduction
	=========================================

	Gerrit is a web-based code review tool built on top of the git version
	control system, but if you've got as far as reading this guide then
	you probably already know that. The purpose of this introduction is to
	allow you to answer the question, is Gerrit the right tool for me?
	Will it fit in my work flow and in my organization?

	What is Gerrit?
	---------------

	I assume that if you're reading this then you're already convinced of
	the benefits of code review in general but want some technical support
	to make it easy. Code reviews mean different things to different people.
	To some it's a formal meeting with a projector and an entire team
	going through the code line by line. To others it's getting someone to
	glance over the code before it is committed.

	Gerrit is intended to provide a light weight framework for reviewing
	every commit before it is accepted into the code base. Changes are
	uploaded to Gerrit but don't actually become a part of the project
	until they've been reviewed and accepted. In many ways this is simply
	tooling to support the standard open source process of submitting
	patches which are then reviewed by the project members before being
	applied to the code base. However Gerrit goes a step further making it
	simple for all committers on a project to ensure that changes are
	checked over before they're actually applied. Because of this Gerrit
	is equally useful where all users are trusted committers such as may
	be the case with closed-source commercial development. Either way it's
	still desirable to have code reviewed to improve the quality and
	maintainability of the code. After all, if only one person has seen
	the code it may be a little difficult to maintain when that person
	leaves.

	Gerrit is firstly a staging area where changes can be checked over
	before becoming a part of the code base. It is also an enabler for
	this review process, capturing notes and comments about the changes to
	enable discussion of the change. This is particularly useful with
	distributed teams where this conversation can't happen face to face.
	Even with a co-located team having a review tool as an option is
	beneficial because reviews can be done at a time that is convenient
	for the reviewer. This allows the developer to create the review and
	explain the change while it is fresh in their mind. Without such a
	tool they either need to interrupt someone to review the code or
	switch context to explain the change when they've already moved on to
	the next task.

	This also creates a lasting record of the conversation which can be
	useful for answering the inevitable "I know we changed this for a
	reason" questions.

	Where does Gerrit fit in?
	-------------------------

	Any team with more than one member has a central source repository of
	some kind (or they should). Git can theoretically work without such a
	central location but in practice there is usually a central
	repository. This serves as the authoritative copy of what is actually in
	the project. This is what everyone fetches from and pushes to and is
	generally where build servers and other such tools get the source
	from.

	.Central Source Repository
	image::images/intro-quick-central-repo.png[Authoritative Source Repository]

	Gerrit is deployed in place of this central repository and adds an
	additional concept, a store of pending changes. Everyone still fetches
	from the authoritative repository but instead of pushing back to it,
	they push to this pending changes location. A change can only be submitted
	into the authoritative repository and become an accepted part of the project
	once the change has been reviewed and approved.

	.Gerrit in place of Central Repository
	image::images/intro-quick-central-gerrit.png[Gerrit in place of Central Repository]

	Like any repository hosting solution, Gerrit has a powerful
	link:access-control.html[access control model.]
	Users can even be granted access to push directly into the central
	repository, bypassing code review entirely. Gerrit can even be used
	without code review, used simply to host the repositories and
	controlling access. But generally it's just simpler and safer to go
	through the review process even for users who are allowed to directly
	push.

	The Life and Times of a Change
	------------------------------

	The easiest way to get a feel for how Gerrit works is to follow a
	change through its entire life cycle. For the purpose of this example
	we'll assume that the Gerrit Server is running on a server called
	+gerrithost+ with the HTTP interface on port +8080+ and the SSH
	interface on port +29418+. The project we'll be working on is called
	+RecipeBook+ and we'll be developing a change for the +master+ branch.

	Cloning the Repository
	~~~~~~~~~~~~~~~~~~~~~~

	Obviously the first thing we need to do is get the source that we're
	going to be modifying. As with any git project you do this by cloning
	the central repository that Gerrit is hosting. e.g.

	----
	$ git clone ssh://gerrithost:29418/RecipeBook.git RecipeBook
	Cloning into RecipeBook...
	----

	Then we need to make our actual change and commit it locally. Gerrit
	doesn't really change anything here, this is just the standard editing
	and git. While not strictly required, it's best to include a Change-Id
	in your commit message so that Gerrit can link together different
	versions of the same change being reviewed. Gerrit contains a standard
	link:user-changeid.html[Change-Id commit-msg hook]
	that will generate a unique Change-Id when you commit. If you don't do
	this then Gerrit will generate a Change-Id when you push your change
	for review. But because you don't have the Change-Id in your commit
	message you'll need to manually copy it in if you need to upload
	another version of your change. Because of this it's best to just
	install the hook and forget about it.

	Creating the Review
	~~~~~~~~~~~~~~~~~~~

	Once you've made your change and committed it locally it's time to
	push it to Gerrit so that it can be reviewed. This is done with a git
	push to the Gerrit server. Since we cloned our local repository
	directly from Gerrit it is the origin so we don't have to redefine the
	remote.

	----
	$ <work>
	$ git commit
	[master 9651f22] Change to a proper, yeast based pizza dough.
	1 files changed, 3 insertions(+), 2 deletions(-)
	$ git push origin HEAD:refs/for/master
	Counting objects: 5, done.
	Delta compression using up to 8 threads.
	Compressing objects: 100% (2/2), done.
	Writing objects: 100% (3/3), 542 bytes, done.
	Total 3 (delta 0), reused 0 (delta 0)
	remote:
	remote: New Changes:
	remote: http://gerrithost:8080/68
	remote:
	To ssh://gerrithost:29418/RecipeBook.git
	* [new branch] HEAD -> refs/for/master
	----

	The only different thing about this is the +refs/for/master+ branch.
	This is a magic branch that creates reviews that target the master
	branch. For every branch Gerrit tracks there is a magic
	+refs/for/<branch_name>+ that you push to to create reviews.

	In the output of this command you'll notice that there is a link to
	the HTTP interface of the Gerrit server we just pushed to. This is the
	web interface where we will review this commit. Let's follow that link
	and see what we get.

	.Gerrit Code Review Screen
	image::images/intro-quick-new-review.jpg[Gerrit Review Screen]

	This is the Gerrit code review screen where someone will come to
	review the change. There isn't too much to see here yet, you can look
	at the diff of your change, add some comments explaining what you did
	and why, you may even add a list of people that should review the change.

	Reviewers can find changes that they want to review in any number of
	ways. Gerrit has a capable
	link:user-search.html[search]
	that allows project leaders (or anyone else) to find changes that need
	to be reviewed. Users can also setup watches on Gerrit projects with a
	search expression, this causes Gerrit to notify them of matching
	changes. So adding a reviewer when creating a review is just a
	recommendation.

	At this point the change is available for review and we need to switch
	roles to continue following the change. Now let's pretend we're the
	reviewer.

	Reviewing the Change
	~~~~~~~~~~~~~~~~~~~~

	The reviewer's life starts at the code review screen shown above. He
	can get here in a number of ways, but for some reason they've decided
	to review this change. Of particular note on this screen are the two
	"Need" lines:

	----
	* Need Verified
	* Need Code-Review
	----

	Gerrit's default work-flow requires two checks before a change is
	accepted. Code-Review is someone looking at the code, ensuring it
	meets the project guidelines, intent etc. Verifying is checking that
	the code actually compiles, unit tests pass etc. Verification is
	usually done by an automated build server rather than a person. There
	is even a
	link:https://wiki.jenkins-ci.org/display/JENKINS/Gerrit+Trigger[Gerrit Trigger Jenkins Plugin]
	that will automatically build each uploaded change and update the
	verified score accordingly.

	It is important to note that Code-Review and Verification are
	different permissions in Gerrit, allowing these tasks to be separated.
	For example, an automated process would have rights to verify but not
	to code-review.

	Since we are the code reviewer, we're going to review the code. To do
	this we can view it within the Gerrit web interface as either a
	unified or side-by-side diff by selecting the appropriate option. In
	the example below we've selected the side-by-side view. In either of
	these views you can add inline comments by double clicking on the line
	(or single click the line number) that you want to comment on. Also you
	can add file comment by double clicking anywhere (not just on the
	"Patch Set" words) in the table header or single clicking on the icon
	in the line-number column header. Once published these comments are
	viewable to all, allowing discussion of the change to take place.

	.Side By Side Patch View
	image::images/intro-quick-review-line-comment.jpg[Adding a Comment]

	Code reviewers end up spending a lot of time navigating these screens,
	looking at and commenting on these changes. To make this as efficient
	as possible Gerrit has keyboard shortcuts for most operations (and
	even some operations that are only accessible via the hot-keys). At
	any time you can hit the +?+ key to see the keyboard shortcuts.

	.Gerrit Hot Key Help
	image::images/intro-quick-hot-key-help.jpg[Hot Key Help]

	Once we've looked over the changes we need to complete reviewing the
	submission. To do this we click the _Review_ button on the change
	screen where we started. This allows us to enter a Code Review label
	and message.

	.Reviewing the Change
	image::images/intro-quick-reviewing-the-change.jpg[Reviewing the Change]

	The label that the reviewer selects determines what can happen next.
	The +1 and -1 level are just an opinion where as the +2 and -2 levels
	are allowing or blocking the change. In order for a change to be
	accepted it must have at least one +2 and no -2 votes.
	Although these are numeric values, they in no way accumulate;
	two +1s do not equate to a +2.

	Regardless of what label is selected, once the _Publish Comments_
	button has been clicked, the cover message and any comments on the
	files become visible to all users.

	In this case the change was not accepted so the creator needs to
	rework it. So let's switch roles back to the creator where we
	started.

	Reworking the Change
	~~~~~~~~~~~~~~~~~~~~

	As long as we set up the
	link:user-changeid.html[Change-Id commit-msg hook]
	before we uploaded the change, re-working it is easy. All we need
	to do to upload a re-worked change is to push another commit that has
	the same Change-Id in the message. Since the hook added a Change-ID in
	our initial commit we can simply checkout and then amend that commit.
	Then push it to Gerrit in the same way as we did to create the review. E.g.

	----
	$ <checkout first commit>
	$ <rework>
	$ git commit --amend
	$ git push origin HEAD:refs/for/master
	Counting objects: 5, done.
	Delta compression using up to 8 threads.
	Compressing objects: 100% (2/2), done.
	Writing objects: 100% (3/3), 546 bytes, done.
	Total 3 (delta 0), reused 0 (delta 0)
	To ssh://gerrithost:29418/RecipeBook.git
	* [new branch] HEAD -> refs/for/master
	----

	Note that the output is slightly different this time around. We don't
	get told about a new review because we're adding to an existing
	review. Having uploaded the reworked commit we can go back into the
	Gerrit web interface and look at our change.

	.Reviewing the Rework
	image::images/intro-quick-review-2-patches.jpg[Reviewing the Rework]

	If you look closely you'll notice that there are now two patch sets
	associated with this change, the initial submission and the rework.
	Rather than repeating ourselves lets assume that this time around the
	patch is given a +2 score by the code reviewer.

	Trying out the Change
	~~~~~~~~~~~~~~~~~~~~~

	With Gerrit's default work-flow there are two sign-offs, code review
	and verify. Verifying means checking that the change actually works.
	This would typically be checking that the code compiles, unit tests
	pass and similar checks. Really a project can decide how much or
	little they want to do here. It's also worth noting that this is only
	Gerrit's default work-flow, the verify check can actually be removed
	or others added.

	As mentioned in the code review section, verification is typically an
	automated process using the
	link:https://wiki.jenkins-ci.org/display/JENKINS/Gerrit+Trigger[Gerrit Trigger Jenkins Plugin]
	or similar. But there are times when the code needs to be manually
	verified, or the reviewer needs to check that something actually works
	or how it works. Sometimes it's just nice to work through the code in a
	development environment rather than the web interface. All of these
	involve someone needing to get the change into their development
	environment. Gerrit makes this process easy by exposing each change as
	a git branch. So all the reviewers need to do is fetch and checkout that
	branch from Gerrit and they will have the change.

	We don't even need to think about it that hard, if you look at the
	earlier screen shots of the Gerrit Code Review Screen you'll notice a
	_download_ command. All we need to do to get the change is copy
	paste this command and run it in our Gerrit checkout.

	----
	$ git fetch http://gerrithost:8080/p/RecipeBook refs/changes/68/68/2
	From http://gerrithost:8080/p/RecipeBook
	* branch refs/changes/68/68/2 -> FETCH_HEAD
	$ git checkout FETCH_HEAD
	Note: checking out 'FETCH_HEAD'.

	You are in 'detached HEAD' state. You can look around, make experimental
	changes and commit them, and you can discard any commits you make in this
	state without impacting any branches by performing another checkout.

	If you want to create a new branch to retain commits you create, you may
	do so (now or later) by using -b with the checkout command again. Example:

	git checkout -b new_branch_name

	HEAD is now at d5dacdb... Change to a proper, yeast based pizza dough.
	----

	Easy as that, we now have the change in our working copy to play with.
	You might be interested in what the numbers of the refspec mean.

	* The first 68 is the id of the change +mod 100+. The only reason
	for this initial number is to reduce the number of files in any given
	directory within the git repository.
	* The second 68 is the full id of the change. You'll notice this in
	the URL of the Gerrit review screen.
	* The 2 is the patch-set within the change. In this example we
	uploaded some fixes so we want the second patch set rather than the
	initial one which the reviewer rejected.

	Manually Verifying the Change
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	For simplicity we're just going to manually verify the change.
	The Verifier may be the same person as the code reviewer or a
	different person entirely. It really depends on the size of the
	project and what works. If you have Verify permission then when you
	click the _Review_ button in the Gerrit web interface you'll be
	presented with a verify score.

	.Verifying the Change
	image::images/intro-quick-verifying.jpg[Verifying the Change]

	Unlike the code review the verify check doesn't have a +2 or -2 level,
	it's either a pass or fail so all we need for the change to be
	submitted is a +1 score (and no -1's).

	Submitting the Change
	~~~~~~~~~~~~~~~~~~~~~

	You might have noticed that in the verify screen shot there are two
	buttons for submitting the score _Publish Comments_ and _Publish
	and Submit_. The publish and submit button is always visible, but will
	only work if the change meets the criteria for being submitted (I.e.
	has been both verified and code reviewed). So it's a convenience to be
	able to post review scores as well as submitting the change by clicking
	a single button. If you choose just to publish comments at this point then
	the score will be stored but the change won't yet be accepted into the code
	base. In this case there will be a _Submit Patch Set X_ button on the
	main screen. Just as Code Review and Verify are different operations
	that can be done by different users, Submission is a third operation
	that can be limited down to another group of users.

	Clicking the _Publish and Submit_ or _Submit Patch Set X_ button
	will merge the change into the main part of the repository so that it
	becomes an accepted part of the project. After this anyone fetching
	the git repository will receive this change as a part of the master
	branch.

	GERRIT
	------
	Part of link:index.html[Gerrit Code Review]